Type II group B streptococci (GBS) have several unusual features. Unlike other GBS, type-specific antibodies seems not to be a critical determinant of infection; opsonization is primarily by complement activation. Many type II GBS bear the c protein on their surface. Protein-positive strains (II/c) are more resistant to phagocytosis and killing than protein-negative strains (II) and also are likely to bind IgA to their surfaces. This is a proposal to explore and relate these features. There are three specific aims: (1) To determine if there are quantitative relationships between GBS binding of 125I-IgA and uptake of 3H- GBS by monolayers of human monocyte-derived macrophages for a collection of type II strains; (2) To identify the principal macrophage receptors for the phagocytosis of type II GBS, using immune complexes and anti-receptor monoclonal antibodies on the culture matrix to attract and engage receptors; (3) To determine if IgA binding by type II GBS is associated with decreased bacterial deposition of C3 and IgG, using ELISA methods and 125I-C3 and 125I-IgG. When the roles of IgA binding, macrophage receptors, C3 and IgG are better understood in these infections, a logical extension would be a developmental study of these factors in early infancy.